Observations of calcium dynamics in cortical secretory vesicles.

Calcium (Ca(2+)) dynamics were evaluated in fluorescently labeled sea urchin secretory vesicles using confocal microscopy. 71% of the vesicles examined exhibited one or more transient increases in the fluorescence signal that was damped in time. The detection of transient increases in signal was dependent upon the affinity of the fluorescence indicator; the free Ca(2+) concentration in the secretory vesicles was estimated to be in the range of ∼10 to 100 μM.

ATP dependence of the non-specific ion channel in Torpedo synaptic vesicles.

Synaptic vesicles of Torpedo electromotor neurons contain a high amount of ATP. The concentration of total ATP is around 120 mM, whereas the free [ATP] is about 5-6 mM. We examined the effect of intravesicular ATP on the non-specific ion channel in Torpedo-fused synaptic vesicles.

Hydrogen ions control synaptic vesicle ion channel activity in Torpedo electromotor neurones.

During exocytosis the synaptic vesicle fuses with the surface membrane and undergoes a pH jump. When the synaptic vesicle is inside the presynaptic nerve terminal its internal pH is about 5.5 and after fusion, the inside of the vesicle comes in contact with the extracellular medium with a pH of about 7.

Apamin-sensitive nitric oxide- and ATP-mediated motor effects on the guinea pig small intestine.

The involvement of nitric oxide and ATP in both spontaneous and electrically-induced nonadrenergic noncholinergic (NANC) motor activity with special interest in the apamin-sensitive mechanisms was studied in a guinea pig ileum model. Depending on the concentration (0.1 or 1 micromol/l), apamin, a blocker of the calcium-activated potassium channels and antagonist of ATP action, induced either TTX (0.

Intracellular calcium dynamics--sparks of insight.

Calcium ions are of key importance in a large number of cellular functions. In the past decade a large variety of cells have been found to show localized increases in the intracellular calcium concentration named calcium sparks. In this brief review, the methodology of detecting calcium sparks by confocal microscopy is summarized.

GABA- and glutamate-mediated network activity in the hippocampus of neonatal and juvenile rats revealed by fast calcium imaging.

In the rat hippocampus, during the first postnatal week, network activity is characterized by GABA-driven giant depolarizing potentials (GDPs) associated with calcium signals that are readily blocked when the GABAA antagonist bicuculline is applied to the bath. Towards the end of the first postnatal week, in concomitance with the shift of GABA responses from the depolarizing to the hyperpolarizing direction, functional glutamatergic connections start appearing. At this developmental stage, application of bicuculline blocks GABAA-mediated inhibition and induces the appearance of interictal epileptiform discharges.

Neuronal calcium sparks and intracellular calcium "noise".

Intracellular calcium ions are involved in many forms of cellular function. To accommodate so many control functions, a complex spatiotemporal organization of calcium signaling has developed. In both excitable and nonexcitable cells, calcium signaling was found to fluctuate.

Ion channels in presynaptic nerve terminals and control of transmitter release.

The primary function of the presynaptic nerve terminal is to release transmitter quanta and thus activate the postsynaptic target cell. In almost every step leading to the release of transmitter quanta, there is a substantial involvement of ion channels. In this review, the multitude of ion channels in the presynaptic terminal are surveyed.

Multitude of ion channels in the regulation of transmitter release.

The presynaptic nerve terminal is of key importance in communication in the nervous system. Its primary role is to release transmitter quanta on the arrival of an appropriate stimulus. The structural basis of these transmitter quanta are the synaptic vesicles that fuse with the surface membrane of the nerve terminal, to release their content of neurotransmitter molecules and other vesicular components.

Presynaptic action of the neurosteroid pregnenolone sulfate on inhibitory transmitter release in cultured hippocampal neurons.

The effects of the neurosteroid pregnenolone sulfate (PS) were studied in 3- to 9-week-old hippocampal cultures from neonatal rats. Cells were voltage clamped using CsCl filled electrodes, while action potentials and excitatory glutamatergic currents were abolished by superfusing with a combination of tetrodotoxin, 6-cyano-7-nitroquinoxaline (CNQX) and 2-amino-5-phosphonopentanoic acid (AP-5). Under these conditions spontaneous GABAergic inhibitory postsynaptic currents (sIPSCs) were seen as inward currents at a holding potential of -70 mV.

Where is the "inverting factor" in hormone secretion from parathyroid cells?

Secretion of hormones and transmitters in the body fall into two general categories. In the majority of the secreting cells, including the presynaptic terminals in the nervous system, an increase in the extracellular calcium causes an increase in secretion. There are two notable exceptions to this general rule: the parathyroid cells and the renal juxtaglomerular cells, where an increase in extracellular calcium leads to a decrease in secretion.

Voltage dependent switch in the activity mode of the K+ channel in presynaptic nerve terminals.

The bursting K+ channel is the most common channel in fused Torpedo presynaptic nerve terminals. It possesses the property of 'statistical memory', demonstrated by non-random probability of channel opening. We examined the voltage dependence of the statistical memory and report that removal of channel inactivation by hyperpolarization abolishes it.

A voltage-dependent and calcium-permeable ion channel in fused presynaptic terminals of Torpedo.

1. We used a preparation of fused presynaptic nerve terminals of Torpedo electromotor nerve and the patch-clamp technique for characterization of single ion channels. We report here of a large, nonselective ion channel which is highly voltage dependent.

The non-specific ion channel in Torpedo ocellata fused synaptic vesicles.

1. Synaptic vesicles were isolated and fused into large structures with a diameter of more than 20 microns to characterize their ionic channels. The 'cell'-attached and inside-out configurations of the patch clamp technique were used.

Oscillations in the activity of a potassium channel at the presynaptic nerve terminal.

1. Periodic oscillations were detected in the activity of single macromolecules: potassium channels. 2.

A voltage-sensitive cation channel present in clusters in lobster skeletal muscle membrane.

The single channel properties of a voltage-sensitive cation channel are described in a study of ion channel activity in enzymatically induced blebs of lobster skeletal muscle membrane. This cation channel, one of several that are spontaneously active in excised patches from bleb membrane, can be distinguished from other channels on the basis of its large single channel conductance (293 pS), voltage-sensitive gating properties, the presence of a subconductance state of the fully open channel, and a weak selectivity for K > Na. At hyperpolarizing voltages, this channel displays flickering or bursting behavior, and a single state of the fully open channel is observed.

Activation and inactivation of the bursting potassium channel from fused Torpedo synaptosomes.

1. The voltage dependence of the bursting potassium channel in fused synaptosomes from Torpedo electric organ was studied in vitro, using the inside-out and the cell-attached configurations of the patch clamp technique. 2.

Ion channel activity in lobster skeletal muscle membrane.

Ion channel activity in the sarcolemmal membrane of muscle fibers is critical for regulating the excitability, and therefore the contractility, of muscle. To begin the characterization of the biophysical properties of the sarcolemmal membrane of lobster exoskeletal muscle fibers, recordings were made from excised patches of membrane from enzymatically induced muscle fiber blebs. Blebs formed as evaginations of the muscle sarcolemmal membrane and were sufficiently free of extracellular debris to allow the formation of gigaohm seals.

Currents and channels in the presynaptic nerve terminal.

Synaptic transmission is a key element in neuronal communication in the nervous system. It is determined by two basic sets of processes: release of transmitter from the presynaptic nerve ending and the detection and response by the postsynaptic cell. The release of transmitter is crucially dependent on the interplay among the ion channels in the surface membrane of the presynaptic terminal.

The methodology for studying coordinated calcium concentration changes in a pancreatic beta cell line.

Intracellular calcium concentration was imaged in beta Tc cells with the aid of Fluo-3 indicator and the Meridian ACAS 570 interactive laser cytometry. This cell line does not respond by an elevation in [Ca2+]in to increase in extracellular [glucose], but does respond to 10 microM forskolin. It was found that forskolin increases the mean [Ca2+]in and produces calcium spikes.

Visualization of synaptic structure and function with confocal microscopy: calcium fluctuations and oscillations.

This article summarizes the basic principles of confocal microscopy and how they can be employed to visualize synaptic structure and function. Optical 'sectioning' of living cells allows the examination of a large number of biological processes at different subcellular localities. Different fluorescent markers enable the study of processes in the extracellular, intracellular and membrane domains of the nerve cell.